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Abstract:

The present invention provides embodiments of methods for performing
inter-technology handoffs in a loosely coupled network architecture. One
embodiment of the method includes configuring a downlink data path from a
target access network to a mobile device concurrently with transmitting a
data path registration request from the target access network to an
anchor point during handoff of the mobile device from a source access
network to the target access network.

Claims:

1. A method for implementation in a target access network, comprising:
configuring a downlink data path from the target access network to a
mobile device concurrently with transmitting a data path registration
request from the target access network to an anchor point during handoff
of the mobile device from a source access network to the target access
network.

4. The method of claim 1, comprising starting a timer at the target
access network in response to configuring the downlink data path and
tearing down the established downlink data path if the timer expires
before the anchor point responds to the data path registration request or
in response to the data path registration request being rejected.

5. The method of claim 4, comprising performing symmetric configuration
of the uplink and downlink data paths after the established downlink data
path is torn down in response to expiration of the timer expiration, said
symmetric configuration being performed in response to receiving a
delayed acceptance of the registration request.

6. The method of claim 1, comprising forwarding at least one downlink
packet to the mobile device prior to or concurrently with receiving a
data path registration response from the anchor point indicating that the
anchor point has switched a data path binding from the source access
network to the target access network.

7. The method of claim 1, comprising completing the data path setup by
configuring an uplink direction data path from the mobile device via the
target access network to the anchor point in response to receiving the
data path registration response.

8. The method of claim 1, comprising forwarding said at least one
downlink packet from the target access network to the mobile device over
the downlink data path prior to or concurrently with configuring the
uplink data path.

9. A method for implementation in a mobile device, comprising: processing
at least one downlink data packet received from a target access network
before receiving a data path registration response indicating that an
anchor point has switched a data path binding from a source access
network to the target access network in response to a request to handoff
the mobile device from the source access network to the target access
network.

10. The method of claim 9, wherein processing said at least one downlink
packet comprises processing said at least one downlink packet at the
mobile device prior to or concurrently with the target access network
receiving a data path registration response indicating that the anchor
point has switched a data path binding from the source access network to
the target access network.

11. The method of claim 10, wherein receiving said at least one downlink
packet comprises receiving said at least one downlink packet concurrently
with the target access network configuring an uplink data path from the
mobile device to the target access network in response to receiving the
data path registration response.

12. The method of claim 9, comprising establishing an uplink data path
between the mobile device and the target access network in response to
the mobile device receiving the data path registration response
indicating that the anchor point has switched the data path binding from
the source access network to the target access network.

13. The method of claim 12, comprising transmitting at least one uplink
packet from the mobile device over the uplink data path between the
mobile device and the target access network.

[0004] A conventional communication system uses one or more access nodes
to provide network connectivity to one or more mobile nodes units or
access terminals. The access nodes may be referred to as access points,
access networks, base stations, base station routers, cells, femtocells,
pico-cells, and the like. For example, in a cellular communication system
that operates according to Long Term Evolution (LTE) standards and/or
High Rate Packet Data (HRPD, eHRPD) standards defined by the Third
Generation Partnership Project (3GPP, 3GPP2), one or more nodes may be
used to provide wireless network connectivity to mobile units The mobile
units may include cellular telephones, personal data assistants, smart
phones, Global Positioning Systems, navigation systems, network interface
cards, notebook computers, desktop computers, other user equipment such
as may be defined in 3GPP standards documentation, mobile stations such
as defined in WiMAX standards documentation, and the like. Numerous types
and generations of wireless communication systems have been developed and
deployed to provide network connectivity to mobile nodes. Exemplary
wireless communication systems include systems that provide wireless
connectivity to micro cells (e.g., systems that provide wireless
connectivity according to the IEEE 802.11, IEEE 802.15, or Wi-Fi
standards) and systems that provide wireless connectivity to macro cells
(e.g., systems that operate according to the 3GPP, 3GPP2 standards and/or
systems operate according to the IEEE 802.16, WiMAX, and IEEE 802.20
standards). Multiple generations of these systems have been deployed
including Second Generation (2G), Third Generation (3G), and Forth
Generation (4G) systems.

[0005] The coverage provided by different service providers in a
heterogeneous communication system may intersect and/or overlap. For
example, a wireless access node for a wireless local area network may
provide network connectivity to mobile nodes in a micro cell or pico-cell
associated with a coffee shop that is within the macro cell coverage area
associated with a base station of a cellular communication system. For
another example, cellular telephone coverage from multiple service
providers may overlap and mobile nodes may therefore be able to access
the wireless communication system using different generations of radio
access technologies, e.g., when one service provider implements a 3G
system and another service provider implements a 4G system. For yet
another example, a single service provider may provide coverage using
overlaying radio access technologies, e.g., when the service provider has
deployed a 3G system and is in the process of incrementally upgrading to
a 4G system.

[0006] Mobile units that roam throughout the wireless communication system
can be handed off between access nodes that operate according to
different radio access technologies. For example, a multi-mode mobile
unit may roam from a macrocell that operates according to the Long Term
Evolution (LTE) or WiMAX radio access network (RAN) standards to a
microcell or hotspot that is served by a WiFi access point. Mobile units
users do not like service interruptions and may be frustrated or annoyed
if they perceive any degradation of the service caused by handing over
between different serving nodes. Service providers therefore set the
provision of seamless roaming across different wireless technologies as a
critically important priority when designing and deploying heterogeneous
networks.

SUMMARY OF CLAIMED EMBODIMENTS

[0007] The disclosed subject matter is directed to addressing the effects
of one or more of the problems set forth above. The following presents a
simplified summary of the disclosed subject matter in order to provide a
basic understanding of some aspects of the disclosed subject matter. This
summary is not an exhaustive overview of the disclosed subject matter. It
is not intended to identify key or critical elements of the disclosed
subject matter or to delineate the scope of the disclosed subject matter.
Its sole purpose is to present some concepts in a simplified form as a
prelude to the more detailed description that is discussed later.

[0008] In one embodiment, a method is provided for performing
inter-technology handoffs in a loosely coupled network architecture. One
embodiment of the method includes configuring a downlink data path from a
target access network to a mobile device concurrently with transmitting a
data path registration request from the target access network to an
anchor point during handoff of the mobile device from a source access
network to the target access network. Another embodiment includes
receiving a downlink packet from a target access network before receiving
a data path registration response indicating that an anchor point has
switched a data path binding from a source access network to the target
access network in response to a request to handoff the mobile device from
the source access network to the target access network.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The disclosed subject matter may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which like reference numerals identify like elements, and in
which:

[0013]FIG. 4 conceptually illustrates a first exemplary embodiment of a
method of performing handoff of a mobile unit between radio access
networks that operate according to different radio access technologies;
and

[0014] FIG. 5 conceptually illustrates a second exemplary embodiment of a
method of performing handoff of a mobile unit between radio access
networks that operate according to different radio access technologies.

[0015] While the disclosed subject matter is susceptible to various
modifications and alternative forms, specific embodiments thereof have
been shown by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description herein of
specific embodiments is not intended to limit the disclosed subject
matter to the particular forms disclosed, but on the contrary, the
intention is to cover all modifications, equivalents, and alternatives
falling within the scope of the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0016] Illustrative embodiments are described below. In the interest of
clarity, not all features of an actual implementation are described in
this specification. It will of course be appreciated that in the
development of any such actual embodiment, numerous
implementation-specific decisions should be made to achieve the
developers' specific goals, such as compliance with system-related and
business-related constraints, which will vary from one implementation to
another. Moreover, it will be appreciated that such a development effort
might be complex and time-consuming, but would nevertheless be a routine
undertaking for those of ordinary skill in the art having the benefit of
this disclosure.

[0017] The disclosed subject matter will now be described with reference
to the attached figures. Various structures, systems and devices are
schematically depicted in the drawings for purposes of explanation only
and so as to not obscure the present invention with details that are well
known to those skilled in the art. Nevertheless, the attached drawings
are included to describe and explain illustrative examples of the
disclosed subject matter. The words and phrases used herein should be
understood and interpreted to have a meaning consistent with the
understanding of those words and phrases by those skilled in the relevant
art. No special definition of a term or phrase, i.e., a definition that
is different from the ordinary and customary meaning as understood by
those skilled in the art, is intended to be implied by consistent usage
of the term or phrase herein. To the extent that a term or phrase is
intended to have a special meaning, i.e., a meaning other than that
understood by skilled artisans, such a special definition will be
expressly set forth in the specification in a definitional manner that
directly and unequivocally provides the special definition for the term
or phrase.

[0018] Generally, the present application describes techniques for
performing handoffs between radio access networks in a loosely coupled
wireless communications network architecture. For example, embodiments of
the techniques described herein can be used to support inter-technology
handoffs between radio access networks (RANs) that operate according to
different radio access technologies. The radio access networks in
loosely-coupled interworking architectures are disjoint and so control
plane or data plane interfaces may not be provided between radio access
networks in the loosely-coupled system. For example, loosely-coupled
heterogeneous networks do not support data tunneling inter-RAN interfaces
between 3G-4G or WiFi RANs during inter-technology handover.
Loosely-coupled interworking architectures are much simpler to implement
because they do not require interworking related changes in the legacy
RAN equipment. Session continuity is maintained via a common Internet
Protocol (IP) Mobility anchor point in the packet core that is a common
anchor point for the radio access networks that operate according to the
radio access technologies supported by the heterogeneous network. In
various embodiments, the common Internet Protocol (IP) Mobility anchor
point can be implemented in entities such as a 3GPP eUTRAN Packet Data
Network (PDN) Gateway (for 2G-3G-4G-WiFi interworking with LTE), a Mobile
IP Home Agent (HA) or Local Mobility Anchor (LMA) used for interworking
of technologies utilizing Mobile IP, and the like.

[0019] The absence of control plane or data plane interfaces between the
radio access networks may lead to delays and/or disruptions during
inter-technology handoffs of mobile devices. For example, a mobile unit
may initiate a handover sequence by transmitting a registration message
via the target radio access network to the common anchor point. The
anchor point switches the data path binding from the source radio access
network to the target radio access network and begins forwarding data
towards the target radio access network concurrently with sending a
registration response, which triggers the target radio access network to
configure the data path between the anchor point to the mobile device.
Transmission and/or processing delays while configuring the downlink data
path from the target access network to the mobile device may cause
streaming packets to be lost. For example, downlink video packets that
are streamed from the anchor point to the mobile device according to the
real-time transport protocol over user datagram protocol (RTP-over-UDP)
may be lost because of a time gap between when the anchor point switches
the binding and when the target access network configures the downlink
data path to the mobile device. Embodiments of the target access network
described herein may therefore configure a downlink data path from the
target access network to a mobile device concurrently with transmitting a
data path registration request from the target access network to an
anchor point during handoff of the mobile device from the source access
network to the target access network.

[0020] FIG. 1 conceptually illustrates a first exemplary embodiment of a
wireless communication system 100. In the illustrated embodiment, a
common core network 105 is electronically and/or communicatively coupled
to a broader network such as the Internet 110. The common core 105
includes a common IP mobility anchor 115 that serves as an anchor point
for one or more radio access networks 120. In the illustrated embodiment,
the common IP mobility anchor 115 performs network layer (L-3) functions
such as network routing, fragmentation and reassembly of packets, and
reporting delivery errors. For example, the common core 105 may function
as a Mobile IP home agent (MIP-HA), a packet data node gateway (PDN-GW),
or other mobility anchor. In the illustrated embodiment, depending upon
the access technology defined standards, the common IP mobility anchor
115 terminates data path tunnels between the anchor 115 and one or more
access networks (nodes) or wireless communication devices such as the
mobile unit 125. Packets that are forwarded along the data paths tunnels
can be addressed in the uplink direction using IP addresses for the
network peers of the mobile unit and in the downlink direction using IP
addresses of the mobile unit 125. The data paths can pass through either
of the radio access networks 120 shown in FIG. 1.

[0021] Each radio access network 120 includes one or more access routers
130 that are coupled to one or more access nodes 135. The access routers
130 implement link layer and/or medium access control layer (L-2)
functionality and can support an L-2 data path over the air interface
between the access nodes 135 and the mobile units 125. For example, the
access routers 130 may function as a mobile IP foreign agent, a proxy
mobile IP client, a General Packet Radio Service (GPRS) tunneling
protocol client, and the like. Exemplary access nodes 135 include base
stations, base station routers incorporating access router functions,
femtocells, WiFi access points, and the like. In the illustrated
embodiment, the radio access networks 120 operate according to different
wireless access technologies. For example, the radio access network
120(1) may operate according to 4G standards (e.g., the 3GPP eUTRAN LTE,
and/or WiMAX standards) and/or protocols and the radio access network
120(2) may operate according to WiFi or 3G standards and/or protocols
(e.g., the 3GPP2 HRPD/eHRPD and/or 3GPP WCDMA-UMTS standards). However,
persons of ordinary skill in the art should appreciate that other
combinations of wireless access technologies may also be used.

[0022] The radio access networks 120 are loosely coupled. As used herein,
the term "loosely coupled" will be understood to mean that control plane
or data plane interfaces have not been provided between the radio access
networks 120 in the system 100. Control plane and data plane signaling
associated with one radio access network 120(1) may not be conveyed to
the other radio access network 120(2) without passing through the common
core 105. Consequently, data paths for the mobile unit 125 are anchored
at the common IP mobility anchor 115, which is also responsible for
switching the data path between the radio access networks 120 during
handoffs of the mobile unit 125. Session continuity is maintained in the
loosely-coupled interworking architecture by making the IP Mobility
anchor point 115 common for all radio access technologies. As shown in
FIG. 1, the anchor point may be implemented in the packet core 105. In
exemplary embodiments, the anchor point 115 may implement a MIP home
agent/LMA or 3GPP-defined packet data network gateway (PDN GW) function
with IP level tunneling towards a local access router 130 in the serving
RAN 120. In one embodiment, the local access router 130 may implement a
3GPP S-GW function with a (possibly separate) control plane mobility
management entity (MME) function, an MIPv4 foreign agent (FA) or MIPv6
access router function, a PMIP client function, and the like. The access
router 130 also supports L2 level tunneling to the mobile device 125 over
the specific RAN 120.

[0023] Loose coupling can be contrasted with tight coupling, which is
characterized by the presence of control plane and/or data plane
interfaces between the radio access networks 120. Loosely coupled
networks are oriented towards dual-radio or multi-mode mobile units that
include two or more independent radio transceivers so that the multi-mode
mobile unit can maintain separate physical layer and data layer
connections to the radio access networks 120. In contrast, tightly
coupled networks are oriented towards single radio mobile units that
maintain physical layer and data layer connections to the tightly coupled
network using a single interface. Some combinations of standards and/or
protocols require loose coupling when they are implemented in the same
heterogeneous network. For example, typical WiFi networks cannot be
tightly coupled to 3G/4G networks because the WiFi air interfaces do not
support the link layer and/or medium access control layer messaging
required for 3G/4G. The loosely-coupled interworking architecture may be
simpler to implement than a tightly coupled system, at least in part
because the loosely coupled system may not require interworking-related
changes in legacy RAN equipment.

[0024] FIG. 2 conceptually illustrates a second exemplary embodiment of a
wireless communication system 200. In the illustrated embodiment, the
wireless communication system 200 includes a home core serving network
205 that includes a Policy and Charging Rules Function (PCRF) server 206,
a billing server 207, a home authentication authorization, and accounting
(AAA) server 208, and a home agent 209 that may serve as the common IP
mobility anchor point for devices within the system 200. The wireless
communication system 200 also may include a visited core network 210 that
may include a visited AAA server 213 and a visited PCRF 214. Techniques
for implementing and operating the elements of the networks 205, 210 are
known in the art and in the interest of clarity only those aspects of
implementing and/or operating the elements of the networks 205, 210 that
are relevant to the claimed subject matter will be discussed herein.
Furthermore, persons of ordinary skill in the art having benefit of the
present disclosure should appreciate that the wireless communication
system 200 may include other elements that are not shown in FIG. 2 in the
interest of clarity.

[0025] The wireless communication system 200 uses a loosely coupled
interworking architecture to support interworking between access
technologies including 3GPP2 High Rate Packet Data (HRPD) technologies,
WiMAX technologies, and WiFi technologies. In the illustrated embodiment,
the HRPD network includes one or more packet data serving nodes (PDSN)
215, which may also serve as a foreign agent for a roaming device that is
anchored at the home agent 209. The PDSN 215 is electronically and/or
communicatively coupled to one or more radio network controllers (RNCs)
220 that may also implement a point coordination function (PCF). The RNC
220 controls and coordinates communication between one or more base
stations 225 and various wireless communication devices such as the
mobile unit 230. The WiFi network includes wireless local area network
gateways (WLAN-GW) 235 that oversee wireless communication between access
points 240 and wireless communication devices such as the mobile unit 230
that operate according to IEEE 802.11 protocols. The WiMAX system
includes access serving networks (ASN) 245 that control access to the
network 210 for devices that are in communication with access nodes 250.
The ASN 245 may also function as a WiMAX gateway and/or foreign agent.
Standards and protocols for implementing and operating HRPD, WiMAX, and
WiFi networks are known in the art and in the interest of clarity only
those aspects to implementing and operating these networks that are
relevant to the claimed subject matter will be discussed herein.

[0026] The HRPD, WiMAX, and WiFi networks in the heterogeneous network 200
are loosely coupled and so the home agent 209 may serve as the mobility
anchor point for wireless devices such as the mobile unit 230. Data path
tunnels between home agent 209 and HRPD and WiMAX radio access networks
may be based upon Mobile IP (CMIP or PMIP). In the illustrated
embodiment, there are no control plane or data plane interfaces between
the HRPD network (e.g., the PDSN 215, the RNC 220, and the base stations
225), the Wifi network (e.g., the WLAN 235 and the access points 240),
and the WiMAX network (e.g., the ASN 245 and the access nodes 250). At
least in part to reduce delays, latency, and jitter during handover of
downlink streaming sessions between the different technologies, routers
in the HRPD, WiMAX, and WiFi networks may be able to configure a downlink
data path from the target access nodes 225, 240, 250 to the wireless
device 230 concurrently with transmitting a data path registration
request to the home agent 209 (or other mobility anchor point in the home
core serving network, CSN 205) during handoff of the device 230 between
the different technologies in the network 200. For example, the PDSN 215,
WLAN-GW 235, and ASN 245 may function as access routers and may be able
to perform the downlink pre-configuration of the associated access nodes
225, 240, 250. In one embodiment, handovers of the mobile device 230 may
be performed according to the flavors of Mobile IP (CMIP or PMIP)
protocols defined by the different wireless access technology standards.

[0027] FIG. 3 conceptually illustrates a third exemplary embodiment of a
wireless communication system 300. In the illustrated embodiment, the
wireless communication system 300 is constructed as a loosely coupled
architecture for interworking an LTE access network 305 as defined by
3GPP and a High Rate Packet Data (HRPD)/Evolved HRPD (eHRPD) access
network 310 as defined by 3GPP2. Data plane and control plane signaling
may not be supported between the access networks 305, 310 and so the
wireless communication system 300 implements a loosely coupled
architecture to support interworking between the different radio access
technologies supported by the access networks 305, 310. The common IP
mobility anchor point may be implemented in a PDN-GW 315 to an Internet
protocol network 320. The anchor point 315 can terminate network level
data flows between the Internet 320 and a dual-mode or multimode mobile
unit 325 that can communicate according to the different technologies
implemented by the access networks 305, 310. The PDN-GW 315 may also
serve as an LMA that implements a home agent function for the mobile unit
325. The mobile unit 325 may therefore roam and be handed off between the
access networks 305, 310.

[0028] In the illustrated embodiment, the access network 305 includes a
serving gateway (SGW) 330, a mobility management entity (MME) 335, and
one or more base stations or eNodeBs 340. In embodiments defined
according to the LTE standards and/or protocols, the MME 335 is a
control-node for the LTE access-network 305 and may be responsible for
idle mode UE tracking and paging procedure including retransmissions. The
MME 335 may support bearer activation/deactivation processes and be also
responsible for choosing the SGW 330 for a UE at the initial attach and
at time of intra-LTE handover involving Core Network (CN) node
relocation. The MME 335 may also be responsible for authenticating the
user and terminating Non-Access Stratum (NAS) signaling. The MME 335 is
the termination point in the network for ciphering/integrity protection
for NAS signaling and handles the security key management. In embodiments
defined according to the LTE standards and/or protocols, the SGW 330
routes and forwards user data packets. The SGW 335 may also manage and
store UE contexts, e.g. parameters of the IP bearer service, and network
internal routing information. The base station 340 may be an eNodeB and
implements the physical layer functionality that supports the air
interfaces with user equipment such as the mobile unit 325.

[0029] In the illustrated embodiment, the access network 310 includes a
HRPD access network with PDSN 345, a radio network controller (RNC) 350,
and a base station 355. The illustrated embodiment also includes an eHRPD
access network with evolved BTS (eBTS) 360, an evolved RNC (eRNC)
function 365, and an HRPD Serving Gateway (HSGW) 370. In embodiments that
operate according to the 3GPP2 standards and/or protocols, the PDSN 345
may act as the connection point between the radio access network 310 and
IP networks 320. The PDSN 345 may also be responsible for managing
point-to-point protocol (PPP) sessions between the mobile provider's core
IP network and the mobile unit 325. The PDSN 345 may therefore also
support mobility management functions and/or packet routing
functionality. In embodiments that operate according to the 3GPP2
standards and/or protocols, the radio network controller 350 is
responsible for controlling the base stations 355 within the access
network 310. The radio network controller 350 is responsible for
performing radio resource management, handling mobility management
functions, and encrypting data before the user data is sent to the mobile
unit 355.

[0030] The access networks 305, 310 in the heterogeneous network 300 are
loosely coupled and so the PDN-GW 315 may serve as the mobility anchor
point for wireless devices such as the mobile unit 325. Data path
tunneling between PDN-GW 315 and the S-GW 330 may be based upon GTP (GPRS
tunneling protocol) tunnels or PMIP tunnels. Data path tunneling between
PDN-GW 315 and the HRPD PDSN 345 may be based upon PMIP or CMIP. In the
illustrated embodiment, control plane or data plane interfaces are not
available for communication between the LTE access network 305 (e.g., the
SGW 330, the MME 335, and the eNodeB 340), the HRPD access network 310
(e.g., the PDSN 345, the RNC 350, and the nodeB 355), and the eHRPD
access network (HSGW 370, the eRNC 365, and the eBTS 360). At least in
part to reduce delays, latency, and jitter during handover of downlink
streaming sessions between the different technologies, routers in the LTE
network 305 and the HRPD/eHRPD networks 310 may be able to configure a
downlink data path from the target access nodes 340, 355, 360 to the
mobile unit 325 concurrently with transmitting a data path registration
request to the PDN gateway 315 (or other mobility anchor point) during
handoff of the device 325 between the different technologies in the
network 300. For example, the SGW 330 may function as an access router
that operates according to GTP, the PDSN 345 may function as an access
router (and foreign agent) that operates according to MIPv4, and the HSGW
370 may function as access router and operate according to PMIP6. These
elements of the access networks 305, 310 may be able to perform downlink
pre-configuration of the associated access nodes 340, 355, 360. In one
embodiment, handovers of the mobile device 325 may be performed according
to the corresponding wireless standard specific flavors of Mobile IP
(CMIP or PMIP) or GTP protocols.

[0031]FIG. 4 conceptually illustrates a first exemplary embodiment of a
method 400 of performing handoff of a mobile unit between radio access
networks that operate according to different radio access technologies.
In the illustrated embodiment, a multi-radio mobile device (MU) applies a
make-before-break procedure for IP connectivity
establishment/registration during the inter-technology handover between a
source access router (S-AR) and a target access router (T-AR). A common
IP anchor point (AP) manages the connectivity establishment/registration
to establish uplink and downlink data paths over the new access
technology. Data is sent and received over the old access technology data
path concurrently with establishment of the new data path. The common IP
anchor point performs a symmetric hand off by switching both the uplink
and the downlink data paths for the mobile unit from the old access
technology RAN to the new access technology RAN in response to receiving
new path registration request.

[0032] In the illustrated embodiment, the mobile unit is accessing the
network via the source access router in the source access network. The
data path includes a first leg 405 between the mobile unit and the source
access router and a second leg 410 between the source access router and
the common mobility anchor point. The data path is configured to support
both uplink and downlink data traffic via the anchor point, as indicated
by the double headed arrows. The mobile unit then establishes (at 415)
over the air connectivity with the target access router, which can later
be used to exchange configuration messages for the make-before-break
procedure to establish a data path over the target access network. The
mobile unit can then transmit (at 420) an IP data path registration
request that serves as a handover trigger. Persons of ordinary skill in
the art having benefit of the present disclosure should appreciate that
the nature and format of the registration request may be access
technology standard specific. For example, if CMIPv4 is used, the
registration request may be a MIPv4 Registration request; if CMIPv6 is
used, the registration request may be MIPv6 Binding Update; if PMIP or
GTP is used, the registration request may be dynamic host configuration
protocol (DHCP) message requesting IP connectivity establishment. The
target access router may then forward (at 425) the registration request
to the common anchor point. Persons of ordinary skill in the art having
benefit of the present disclosure should appreciate that the nature and
format of the request transmitted between the target access router and
the common anchor point may be access technology standard specific. For
example, if CMIP or PMIP is used, the registration message that is
transmitted (at 425) may be a MIPv4 Registration request or MIPv6 Binding
Update, whereas if GTP is used, the registration message would be a GTP
specific message.

[0033] In response to receiving (at 425) the registration request, the
anchor point may switch (at 430) the binding of the uplink and downlink
data path to the mobile unit from the source access router to the target
access router. The anchor point may also initiate procedures to tear down
the uplink and downlink data path tunnels to the source access router in
response to receiving the registration message. In the illustrated
embodiment, the common anchor point concurrently performs two actions in
response to switching (at 430) the binding of the mobile unit: (1) the
anchor point begins to transmit the available downlink data packets
towards the target access router over a downlink 435 and (2) the anchor
point transmits (at 440) a response confirming the registration request
to the target access router. Although the right-hand side of the tunnel
(435) is programmed at the anchor point once the binding has been
switched (at 430), the target access router does not program the leg of
the downlink towards the mobile unit until it has received and processed
the registration reply. Consequently, downlink traffic to the mobile unit
may be dropped until the target access router is able to configure the
downlink data path.

[0034] The target access router performs (at 445) a symmetric
configuration of the uplink and downlink data paths in response to
receiving the reply (at 440). The target access router also transmits (at
450) configuration information to the mobile unit that can be used to
configure both the uplink and the downlink data paths. The mobile unit
can use this information to configure the data paths and establish the
link 455 between the mobile unit and the target access router. At this
point, uplink and downlink traffic can be communicated between the mobile
unit and the network peers via the anchor point, as indicated by the
double headed arrows. As discussed herein, the first exemplary embodiment
of the method 400 results in a time gap during which downlink data
packets may be lost. The time gap is a function of the transmission time
between the common anchor point and the target access router and the
processing time of the registration response and the associated data path
configuration at the target radio access network. In some embodiments,
the time gap may be in the range 20-100 msec. Downlink data transmitted
during the time gap is lost and may not be recoverable, particularly for
time-sensitive, data-intensive applications that do not implement
retransmission techniques such as automatic repeat request (ARQ, HARQ).
One exemplary time-sensitive, data-intensive application that is widely
used is video streaming over UDP. Video servers for the video streams do
not implement retransmission for lost data. High resolution video streams
can be transmitted at data rates up to 10 Mb/sec. Consequently, losing
20-100 msec of downlink data may result in a total data loss of 1 Mb.
This lost data prevents seamless user experience for video stream
application.

[0035] FIG. 5 conceptually illustrates a second exemplary embodiment of a
method 500 of performing handoff of a mobile unit (MU) between radio
access networks that operate according to different radio access
technologies. In the illustrated embodiment, a multi-radio mobile unit
(MU) applies a make-before-break procedure for IP connectivity
establishment/registration during the inter-technology handover between a
source access router (S-AR) and a target access router (T-AR). A common
IP anchor point (AP) manages the connectivity establishment/registration
to establish uplink and downlink data paths over the new access
technology. Data is sent and received over the old access technology data
path concurrently with establishment of the new data path. The common IP
anchor point performs hand off by switching the downlink and uplink data
path tunnels for the mobile unit from the old access technology RAN to
the new access technology RAN.

[0036] In the illustrated embodiment, the mobile unit is accessing the
network via the source access router in the source access network. The
data path includes a first leg 505 between the mobile unit and the source
access router and a second leg 510 between the source access router and
the common mobility anchor point. The data path is configured to support
both uplink and downlink data traffic via the anchor point, as indicated
by the double headed arrows. The mobile unit then establishes (at 515)
over the air connectivity with the target access router, which can later
be used to exchange control signaling messages for the make-before-break
procedure to establish a data path over the target access network. The
mobile unit can then transmit (at 520) an IP data path registration
request that serves as a handover trigger. In one embodiment, the IP data
path registration request includes the IP address of the mobile unit. For
example, the mobile unit may request transfer of the same IP address that
it had on the source access technology to the target access technology.
In that case, the IP address of the mobile unit is conveyed to the target
access network by information in the registration message. Persons of
ordinary skill in the art having benefit of the present disclosure should
appreciate that the nature and format of the registration request may be
access technology standard specific. For example, if MIP is used, the
registration request may be a MIPv4 Registration request or MIPv6 Binding
Update and if PMIP or GTP is used, the registration request would be
dynamic host configuration protocol (DHCP) message requesting
registration.

[0037] In response to receiving the registration request from the mobile
unit, the target access router configures (at 525) a downlink data path
530 from the target access router via target access network (including
over the air link) to the mobile unit. For example, the registration
request message may include an IP address or other identifier of the
mobile unit that can be used to configure the downlink data path. In one
embodiment, the target access network may use downlink flow
classification information (e.g. for the QoS flows) that is available
when IP registration is initiated. This information may be used instead
of or in addition to other configuration information. For example, if QoS
flows were established prior to the target access network sending a
registration message to the IP anchor point, the QoS information can be
used to configure the downlink data path. This configuration may be
referred to as an asymmetric data path configuration because the downlink
data path is configured independently of the uplink data path and
configuration of the uplink and downlink data paths does not occur
concurrently or in response to the same signals or messages. The target
access router may also forward (at 535) the registration request to the
common anchor point. Persons of ordinary skill in the art having benefit
of the present disclosure should appreciate that the nature and format of
the request transmitted between the target access router and the common
anchor point may be access technology standard specific. For example, if
CMIP or PMIP is used, the registration message that is transmitted (at
535) may be a MIPv4 Registration request or MIPv6 Binding Update, whereas
if GTP is used, the registration message would be a GTP specific message.

[0038] In response to receiving (at 535) the registration request, the
anchor point may switch (at 540) the binding of the uplink and downlink
data path to the mobile unit from the source access router to the target
access router. The anchor point may also initiate procedures to tear down
the uplink and downlink data path tunnels to the source access router in
response to receiving the registration request. In the second exemplary
embodiment, the common anchor point concurrently performs two actions in
response to switching (at 540) the binding of the mobile unit: (1) the
anchor point begins to transmit the available data packets towards the
target access router over a downlink 545 and (2) the anchor point
transmits (at 550) a response confirming the registration request to the
target access router. In contrast to the first exemplary embodiment
depicted in FIG. 4, both legs 530, 545 of the downlink path may be
programmed by the time downlink packets are ready to be transmitted in
response to the binding having been switched (at 540). Consequently,
downlink traffic transmitted from the anchor point (as indicated by the
boldfaced arrows) may be successfully received by the mobile unit
concurrently (or even before) with the target access router receiving and
processing the response 550 and before the target access router
configures the uplink data path from the mobile unit to the target access
router. In one embodiment, a timer may be started when the data path link
530 is configured and the data path link 530 may be torn down if no
response is received from the anchor point before expiration of the timer
or if the registration fails. The timer may therefore be used to conserve
air interface resources by tearing down the tunnel 530 when the handover
is delayed, interrupted, or fails. In one embodiment, a data path may
subsequently be established according to the conventional "symmetric"
techniques in cases when the timer expires and the data path link 530 is
torn down. In one embodiment, the data path may be subsequently
established according to the conventional symmetric techniques when a
response message indicating acceptance of the request is delayed until
after expiration of the timer and consequently received after the
datapath link 530 has been torn down.

[0039] The target access router performs (at 555) the asymmetric
configuration of the uplink data path in response to receiving the reply
(at 550). The target access router also transmits (at 560) the
registration reply containing configuration information to the mobile
unit that can be used to configure the uplink data path. The mobile unit
can use this information to configure the uplink data path so that the
mobile unit can transmit packets on the uplink. At this point, uplink and
downlink traffic can be communicated between the mobile unit and the
network peers (tunneled via target access network to the anchor point),
as indicated by the double headed arrows. Implementing the asymmetric
configuration of the uplink and downlink data paths at different points
in the handoff procedure can reduce or eliminate the time gap during
which downlink data packets may be lost at least in part because the
tunnel 530 from the target access router to the mobile unit has been
"optimistically" preconfigured so that it is available to carry downlink
data packets as soon as the anchor points switches (at 540) the binding.
Embodiments of the method 500 may therefore be used to support seamless
user experience for time-sensitive, data-intensive application such as
high data rate video streaming applications.

[0040] Portions of the disclosed subject matter and corresponding detailed
description are presented in terms of software, or algorithms and
symbolic representations of operations on data bits within a computer
memory. These descriptions and representations are the ones by which
those of ordinary skill in the art effectively convey the substance of
their work to others of ordinary skill in the art. An algorithm, as the
term is used here, and as it is used generally, is conceived to be a
self-consistent sequence of steps leading to a desired result. The steps
are those requiring physical manipulations of physical quantities.
Usually, though not necessarily, these quantities take the form of
optical, electrical, or magnetic signals capable of being stored,
transferred, combined, compared, and otherwise manipulated. It has proven
convenient at times, principally for reasons of common usage, to refer to
these signals as bits, values, elements, symbols, characters, terms,
numbers, or the like.

[0041] It should be borne in mind, however, that all of these and similar
terms are to be associated with the appropriate physical quantities and
are merely convenient labels applied to these quantities. Unless
specifically stated otherwise, or as is apparent from the discussion,
terms such as "processing" or "computing" or "calculating" or
"determining" or "displaying" or the like, refer to the action and
processes of a computer system, or similar electronic computing device,
that manipulates and transforms data represented as physical, electronic
quantities within the computer system's registers and memories into other
data similarly represented as physical quantities within the computer
system memories or registers or other such information storage,
transmission or display devices.

[0042] Note also that the software implemented aspects of the disclosed
subject matter are typically encoded on some form of program storage
medium or implemented over some type of transmission medium. The program
storage medium may be magnetic (e.g., a floppy disk or a hard drive) or
optical (e.g., a compact disk read only memory, or "CD ROM"), and may be
read only or random access. Similarly, the transmission medium may be
twisted wire pairs, coaxial cable, optical fiber, or some other suitable
transmission medium known to the art. The disclosed subject matter is not
limited by these aspects of any given implementation.

[0043] The particular embodiments disclosed above are illustrative only,
as the disclosed subject matter may be modified and practiced in
different but equivalent manners apparent to those skilled in the art
having the benefit of the teachings herein. Furthermore, no limitations
are intended to the details of construction or design herein shown, other
than as described in the claims below. It is therefore evident that the
particular embodiments disclosed above may be altered or modified and all
such variations are considered within the scope of the disclosed subject
matter. Accordingly, the protection sought herein is as set forth in the
claims below.